arXiv subjects

Masatoshi Fukushima

Publications and source records attributed to Masatoshi Fukushima.

7 recordsLinked to original sources

arXiv2016

Reflections at infinity of time changed RBMs on a domain with Liouville branches

Let $Z$ be the transient reflecting Brownian motion on the closure of an unbounded domain $D\subset {\mathbb R}^d$ with $N$ number of Liouville branches. We consider a diffusion $X$ on $\overline D$ having finite lifetime obtained from $Z$ by a time change. We show that $X$ admits only a finite number of possible symmetric conservative diffusion extensions $Y$ beyond its lifetime characterized by possible partitions of the collection of $N$ ends and we identify the family of the extended Dirichlet spaces of all $Y$ (which are independent of time change used) as subspaces of the space ${\rm BL}(D)$ spanned by the extended Sobolev space $H_e^1(D)$ and the approaching probabilities of $Z$ to the ends of Liouville branches.

math.PR↗

arXiv2016

Stochastic Komatu-Loewner evolutions and SLEs

Let $D={\mathbb H}\setminus \bigcup_{j=1}^N C_j$ be a standard slit domain, where ${\mathbb H}$ is the upper half plane and $C_j,1\le j\le N,$ are mutually disjoint horizontal line segments in ${\mathbb H}$. A stochastic Komatu-Loewner evolution denoted by ${\rm SKLE}_{α,b}$ has been introduced in \cite{CF} as a family $\{F_t\}$ of random growing hulls with $F_t\subset D$ driven by a diffusion process $ξ(t)$ on $\partial {\mathbb H}$ that is determined by certain continuous homogeneous functions $α$ and $b$ defined on the space ${\cal S}$ of all labelled standard slit domains. We aim at identifying the distribution of a suitably reparametrized ${\rm SKLE}_{α,b}$ with that of the Loewner evolution on ${\mathbb H}$ driven by the path of a certain continuous semimartingale and thereby relating the former to the distribution of ${\rm SLE}_{α^2}$ when $α$ is a constant. We then prove that, when $α$ is a constant, ${\rm SKLE}_{α,b}$ up to some random hitting time and modulo a time change has the same distribution as ${\rm SLE}_{α^2}$ under a suitable Girsanov transformation. We further show that a reparametrized ${\rm SKLE}_{\sqrt{6},-b_{\rm BMD}}$ has the same distribution as ${\rm SLE}_6$, where $b_{\rm BMD}$ is the BMD-domain constant indicating the discrepancy of $D$ from ${\mathbb H}$ relative to Brownian motion with darning (BMD in abbreviation). A key ingredient of the proof is a hitting time analysis for the absorbing Brownian motion on ${\mathbb H}.$ We also revisit and examine the locality property of ${\rm SLE}_6$ in several canonical domains. Finally K-L equations and SKLEs for other canonical multiply connected planar domains than the standard slit one are recalled and examined.

math.PR↗

arXiv2016

Stochastic Komatu-Loewner evolutions and BMD domain constant

Let $D={\mathbb H} \setminus \cup_{k=1}^N C_k$ be a standard slit domain, where ${\mathbb H}$ is the upper half plane and $C_k$, $1\leq k\leq N$, are mutually disjoint horizontal line segments in $H$. Given a Jordan arc $γ\subset D$ starting at $\partial H$, let $g_t$ be the unique conformal map from $D\setminusγ[0,t]$ onto a standard slit domain $D_t={\mathbb H} \setminus \cup_{k=1}^N C_k(t)$ satisfying the hydrodynamic normalization at infinity. It has been established recently that $g_t$ satisfies an ODE called a Komatu-Loewner equation in terms of the complex Poisson kernel of the Brownian motion with darning (BMD) for $D_t$. We randomize the Jordan arc $γ$ according to a system of probability measures on the family of equivalence classes of Jordan arcs that enjoy a domain Markov property and a certain conformal invariance property. We show that the induced process $(ξ(t), {\bf s}(t))$ satisfies a Markov type stochastic differential equation, where $ξ(t)$ is a motion on $\partial {\mathbb H}$ and ${\bf} s(t)$ represents the motion of the endpoints of the slits $\{C_k(t),\; 1\le k\le N \}.$ Conversely, given such functions $α$ and $b$ with local Lipschitz continuity, the corresponding SDE admits a unique solution $(ξ(t), {\bf s}(t))$. The latter produces random conformal maps $g_t(z)$ via the Komatu-Loewner equation. The resulting family of random growing hulls $\{F_t\}$ from the conformal mappings is called ${\rm SKLE}_{α,b}.$ We show that it enjoys a certain scaling property and a domain Markov property. Among other things, we further prove that ${\rm SKLE}_{α,-b_{\rm BMD}}$ for a constant $α>0$ has a locality property if and only if $α= \sqrt{6}$, where $b_{\rm BMD}$ is a BMD-domain constant that describes the discrepancy of a standard slit domain from ${\mathbb H}$ relative to BMD.

math.PR↗

arXiv2012

Jump-type Hunt processes generated by lower bounded semi-Dirichlet forms

Let $E$ be a locally compact separable metric space and $m$ be a positive Radon measure on it. Given a nonnegative function $k$ defined on $E\times E$ off the diagonal whose anti-symmetric part is assumed to be less singular than the symmetric part, we construct an associated regular lower bounded semi-Dirichlet form $η$ on $L^2(E;m)$ producing a Hunt process $X^0$ on $E$ whose jump behaviours are governed by $k$. For an arbitrary open subset $D\subset E$, we also construct a Hunt process $X^{D,0}$ on $D$ in an analogous manner. When $D$ is relatively compact, we show that $X^{D,0}$ is censored in the sense that it admits no killing inside $D$ and killed only when the path approaches to the boundary. When $E$ is a $d$-dimensional Euclidean space and $m$ is the Lebesgue measure, a typical example of $X^0$ is the stable-like process that will be also identified with the solution of a martingale problem up to an $η$-polar set of starting points. Approachability to the boundary $\partial D$ in finite time of its censored process $X^{D,0}$ on a bounded open subset $D$ will be examined in terms of the polarity of $\partial D$ for the symmetric stable processes with indices that bound the variable exponent $α(x)$.

math.PR↗

arXiv2008

On unique extension of time changed reflecting Brownian motions

Let $D$ be an unbounded domain in $\RR^d$ with $d\geq 3$. We show that if $D$ contains an unbounded uniform domain, then the symmetric reflecting Brownian motion (RBM) on $\overline D$ is transient. Next assume that RBM $X$ on $\overline D$ is transient and let $Y$ be its time change by Revuz measure ${\bf 1}_D(x) m(x)dx$ for a strictly positive continuous integrable function $m$ on $\overline D$. We further show that if there is some $r>0$ so that $D\setminus \overline {B(0, r)}$ is an unbounded uniform domain, then $Y$ admits one and only one symmetric diffusion that genuinely extends it and admits no killings. In other words, in this case $X$ (or equivalently, $Y$) has a unique Martin boundary point at infinity.

math.PR↗

arXiv2006

Traces of symmetric Markov processes and their characterizations

Time change is one of the most basic and very useful transformations for Markov processes. The time changed process can also be regarded as the trace of the original process on the support of the Revuz measure used in the time change. In this paper we give a complete characterization of time changed processes of an arbitrary symmetric Markov process, in terms of the Beurling--Deny decomposition of their associated Dirichlet forms and of Feller measures of the process. In particular, we determine the jumping and killing measure (or, equivalently, the Lévy system) for the time-changed process. We further discuss when the trace Dirichlet form for the time changed process can be characterized as the space of finite Douglas integrals defined by Feller measures. Finally, we give a probabilistic characterization of Feller measures in terms of the excursions of the base process.

math.PR↗

arXiv2005

Time changes of symmetric diffusions and Feller measures

We extend the classical Douglas integral, which expresses the Dirichlet integral of a harmonic function on the unit disk in terms of its value on boundary, to the case of conservative symmetric diffusion in terms of Feller measure, by using the approach of time change of Markov processes.

math.PR↗